The title compound, C18H25NO4S, is the single adduct obtained from the reac
tion between the N-(tert-butoxy-carbonyl)-L-proline methyl eater and the an
ion of (+)-(R)-methyl p-tolyl sulfoxide. The pyrrolidine ring has a twist c
onformation and the Re face of the carbonyl group is partially blocked by t
he tert-butoxycarbonyl and sulfinyl groups.